I'm not sure Microsoft came too late to the party. Perhaps MSBuild is a bit crappy (I don't know, never used it), but I can imagine Roslyn becoming more useful now on other platforms since it's open sourced. It'll be great that one can be sure the runtime behaves the same on all platforms Roslyn will run on. And it'll also be nice if new runtime features will be available on every platform at (more or less) the same time. I think Roslyn could have a nice future ahead. Personally speaking, I find writing C# is much more enjoyable as writing Java.

And who knows, maybe someone will build a decent MSBuild replacement. Or perhaps the Xamarin guys already have a nice alternative.